How do I read my manure test?
Guidance on interpreting N content from manure testing
Type of N reported
If the manure nutrient report provides Total N, that value should be used directly in USDA FD-CIC. If the manure nutrient report provides separate values for Total Kjeldahl N, nitrite N, and nitrate N, the Total N must be calculated from those values using the following equation:
Total N = Total Kjeldahl N + Nitrite N + Nitrate N
If the manure test provides only Total Kjeldahl N (TKN), or Total Kjeldahl N broken out by Organic N and ammonium, Total Kjeldahl N (the sum of Organic N and ammonium N) may be entered into the Total N input cell.
As-sampled versus dry weight results
Most agricultural labs report manure testing results on an as-sampled basis that can be entered directly into USDA FD-CIC. If the results are reported on a dry-weight basis the analyses will have to be converted back to as-sampled to be entered into USDA FD-CIC. (If it is unclear from the laboratory report if the results are reported on an as-sampled basis, contact the laboratory for clarification.) To convert nutrient content from a dry-weight basis back to an as-sampled basis, use the following equation:
Nutrient content (as-applied basis) = nutrient content (dry basis) × [1 - (moisture content (%) ÷ 100)]
Conversion of units for N content
Units for N content of manure should be entered as lbs N/ton for solid manures and lbs N/1000 gals for liquid manures. It may be necessary to convert units appearing on the manure nutrient test. Some relevant conversions appear in the table below:
| Manure type | Starting unit | Multiply by | To get |
|---|
| Solid manure | % | ×20 | lbs/ton |
| Solid manure | ppm | ×0.002 | lbs/ton |
| Liquid manure | % | ×83.4 | lbs/1,000 gallons |
| Liquid manure | ppm | ×0.00834 | lbs/1,000 gallons |
Sample calculations
(a) % dry weight (dwt) to lbs N/ton as-sampled, solid manure
lb N/ton (as sampled) = ((1 - % Moisture)/100) × (% N in dwt/100) × 2000 lb/ton
(b) % dry weight (dwt) to lbs N/1000 gallon as-sampled, liquid manure
lb N/1000 gal (as sampled) = ((1 - % Moisture)/100) × (% N in dwt/100) × (8.34 lb/gal × 1000)
(c) ppm dry weight (dwt) to lbs N/ton as-sampled, solid manure
lb N/ton (as sampled) = ((1 - % Moisture)/100) × (ppm N in dwt/1000000) × 2000 lb/ton
(d) ppm dry weight (dwt) to lbs N/1000 gallon as-sampled, liquid manure
lb N/1000 gal (as sampled) = ((1 - % Moisture)/100) × (ppm N in dwt/1000000) × (8.34 lb/gal × 1000)
Source: USDA FD-CIC User Guide, Appendix 1 (verbatim)